DESIGN AND SYNTHESIS OF NEW MULTIFUNCTIONAL

EUROPIUM MOLECULAR COMPLEX FOR OLEDS

A Report Submitted

for

Partial fulfilment Master of Science Degree

Under the Guidance of

Dr. Vaidyanathan Sivakumar

Submitted by

Ajit Kumar Pallei

Roll No. 412CY2018

DEPARTMENT OF CHEMISTRY

NATIONAL INSTITUTE OF TECHNOLOGY

ROUKELA, ODISHA - 769008

MAY 2014

ii

DECLARATION

I hereby declare that the project work entitled, “DESIGN AND SYNTHESIS OF NEW

MULTIFUNCTIONAL EUROPIUM MOLECULAR COMPLEX FOR OLEDS”

submitted to NIT Rourkela, is an original work done under guidance of Dr. Vaidyanathan

Sivakumar, Assistant Professor, Department of Chemistry, NIT Rourkela, and this project

work is submitted in the partial fulfilment of the requirements for the award of Master of

Science degree in Chemistry. The results incarnated in this thesis have not been

submitted to any other institute for any other degree.

Date: 06/05/2014 (Ajit Kumar Pallei)

412CY2018

NIT Rourkela

iii

Department of Chemistry

National Institute of Technology, Rourkela

THESIS CERTIFICATE

This is to certify that the thesis entitled “DESIGN AND SYNTHESIS OF NEW

MULTIFUNCTIONAL EUROPIUM MOLECULAR COMPLEX FOR OLEDS”

submitted by Mr. Ajit Kumar Pallei to the National Institute of Technology, Rourkela for

the award of degree of Master of Science is a bonafide record of research work carried out by

her under my supervision. The contents of this thesis, in full or in parts, have not been

submitted to any other Institute or University for the award of any degree or diploma.

Rourkela 769 008 Research Guide

Date: 06/05/2014

Dr. V. SIVAKUMAR

iv

ACKNOWLEDGEMENTS

I take this opportunity to express my profound gratitude and deep regards to my guide

Dr. Vaidyanathan Sivakumar for his exemplary guidance, monitoring and constant

encouragement throughout the course of this thesis. The blessing, help and guidance

given by him time to time shall carry me a long way in the journey of life on which I am

about to embark.

I would like to thank Dr. Niranjan Panda, Head, Department of Chemistry, and all the

faculty members of Department of Chemistry for their constant support and

encouragement in each and every step during my project.

My thanks and appreciations also go to Mr Rajamouli Boddula who helped me in

developing the project and implementing the experiments during my course work and my

lab mates Mr. Aravind, Mis. Kasturi, Mr. Jairam, Mr. Suraj Kumar and other

research scholars at Department of Chemistry, who have willingly helped me out with

their abilities.

Lastly, I thank almighty, my parents, family and friends for their constant encouragement

without which this assignment would not be possible.

(Ajit Kumar Pallei)

v

TABLE OF CONTENTS

SL. No. Contents Page No.

Acknowledgement …………………………………………………………… iv

Abstract ……………………………………………………………………… vii

1 Introduction ………………………………………………………. 1

1.1 Incandescence……………………………………………………. 1

1.2 Luminescence ……………………………………………………. 1

1.3 Triboluminescence ……………………………………………….. 2

1.4 Chemiluminescence …..…………………………………………. 2

1.5 Bioluminescence…. ……………………………………………... 2

1.6 Electroluminescence ……….…………………………………… 2

1.7 Fluorescence ……………………………………………………. 3

1.8 Phosphorescence ………………………………………………… 4

2 Lanthanides ……………………………………………………... 4

2.1 Classic DiekeDiagram for Lanthanide ions ………………………. 5

3. Organic light-emitting diode (OLED)…………………………….. 6

3.1 History of OLEDs ………………………………………………... 7

3.2. Types of OLEDs ………………………………………………….. 7

3.3 Architecture of OLEDs ………………………………………… 8

3.4 Advantages and Applications OLEDs…………………………….. 8

4. Bipolar ligand……………………………………………………... 9

5. Objectives of the work …………………………………………. 10

6. Experimental section………………………………………….... 11

6.1 General Information for synthesis………………………………… 11

6.2 Measurements……………………………………………………... 11

6.3 Experimental procedure ………………………………………… 11

6.4 Experimental Procedure …………………………………………. 13

7. Results and Discussion …………………………………………… 17

8. Summary and Conclusions ……………………………………….. 21

9. Scope for the future work ………………………………………… 21

10. References ……………………………………………………… 22

vi

LIST OF FIGURES

SL. No. Figure name Page No.

1. Types of light based on source……………………………………… 1

2. Jablonski diagram…………………………………………………… 3

3. Simplified mechanism for emission process………………………... 4

4. Classic Dieke diagram………………………………………………. 6

5 OLED device structure……………………………………………… 8

6. Normal energy level diagram of Eu(III) ion………………………… 9

7. Bipolar ligands………………………………………………………. 9

8. Scheme of synthesis for designed new efficient red emitter………... 12

9. Europium complex and Eu(TTA)3 under normal light and UV-light

(365nm)………………………………………………………………

18

10. The UV-visible absorption spectra of Europium complex and

Eu(TTA)3 in chloroform solution…………………………………

18

11. The photoluminescence emission spectra of Eu(TTA)3.2H2O,

Eu(TTA)3Phen-FL-TPA-DPA and Phen-Fl-TPA-DPA

19

12. Thermogravimetric analysis (TGA) for Phen-Fl-TPA-DPA and

Eu(TTA)3Phen-FL-TPA-DPA

20

LIST OF TABLES

SL. No. Name of table Page No.

1. Different types of luminescence………...…………………. 2

2. Types of OLEDs…………………………………………………… 7

vii

ABSTRACT

Key words: TPA-DPA, Fluorene, 1,10-Phenanthroline, π-π* transition

Lanthanide based OLEDs are gained much importance due to their line like emission

characteristics (f-f electronic transition) as well as phosphorescent visible range emission

(IQE up to 100%). Most of the hole transporting materials reported are derived from aromatic

amines, where the inclusion of arylamine units into the antenna should improve the hole

injection/transporting properties of the EuIII-phosphors. The present research work aim is to

increase the internal quantum efficiency by using chromophore (fluorene) molecule in order

to improve the π-π* transition in the antenna and facilitate the energy transfer to europium

ion, to link multi-functional ligands (TPA-DPA/ Fluorene and phenanthroline) that should be

active as well as capable of charge transport. To fulfil this, a new efficient red emitting

europium(III) molecular complex having neutral ligand [Eu(TTA)3 (Phen-Fl-TPA-DPA) -

Eu(TTA)3 = Tris (thenoyltrifluoroacetone) Europium (III), Phen-Fl-TPA-DPA = N1-(4-

(diphenylamino)phenyl)-N1-(4-(1-(9,9-diethyl-9H-fluoren-2-yl)-1H-imidazo[4,5-

f][1,10]phenanthrolin-2-yl)phenyl)-N4,N4-diphenylbenzene-1,4-diamine) has been designed.

The same has been successfully synthesised and optically characterised. The photophysical

studies of the synthesized Ligand (Phen-FL-TPA-DPA) and Eu-complex have been carried

out in the solution form by UV-Vis spectroscopy and spectrofluorimetry. The

photoluminescence emission spectra of Eu(TTA)3Phen-FL-TPA-DPA exhibits 5D0-7FJ (J=0-

4) transitions of Eu(III) ion. The characteristic emission observed at 612 nm due to 5D0-7F2

electric-dipole transition (non-centrosymmetric site). The thermogravimetric analysis (TGA)

shows that the compound is thermally stable (278oC (10%)) and it is good enough to fabricate

the OLED device using the synthesised Eu(III)-complex.

.

1. Introduction:

Light is a form of energy, another form of energy is required to get light. There are two

common ways for the production of light is incandescence and luminescence [1].

Fig. 1 Types of light based on source

1.1 Incandescence of light is nothing but heat energy. When heat something at high

temperature, it will arise to glow. The metal in a flame begin to glow "red hot", that is

incandescence. The tungsten filament of an ordinary incandescent light bulb is heated up to

hotter, it glows brightly that is "white hot". It can see in sun and stars glow by incandescence

[2].

1.2 Luminescence is also called as "cold light" that can be emitted at normal and lower

temperatures. Luminescence is an emission of light it comes when the de-excitation of

electron from the excited state to ground state i.e. when an electromagnetic radiation is

applied to solid or gaseous materials excites the molecules and the substance glows. It have

with few exceptions, the excitation energy is always greater than the energy (wavelength,

color) of the emitted light. There are several varieties of luminescence, each named according

to the source of energy, or the trigger for the luminescence [3]. The different types of

luminescence process are mentioned in the table 1 based on their excitation source.

2

Table 1. Different types of luminescence

Type Excitation Source Example

Bioluminescence Bio-chemical energy firefly, Photinus pyralis

Cathodoluminescence Cathode rays ( high energy

electrons )

microscopea

Chemiluminescence Chemical reaction energy luminol + hydrogen peroxide

→ 3-aminophthalate+ light

Electroluminescence Applied voltage OLEDs

Photoluminescence Photons ( UV, Visible )

Radioluminescence X-rays, γ rays, etc Radium salt

Sonoluminescence Sound waves Bubbles in liquid

Thermoluminescence Thermal stimulation of emission

which is excited by some other

means.

Sediment grains

Triboluminescence Mechanical energy such as

grinding, stress, etc.

Diamond

1.3 Triboluminescence is phosphorescence that is generated by mechanical action. This can

observed when the breaking of chemical bands in a material.

1.4 Chemiluminescence is light, as a result of chemical reaction. Examples of

chemiluminescencea are glow-in-the-dark plastic tubes sold in amusement parks.

1.5 Bioluminescence is luminescence caused by chemical reactions in living things; it is a

form of chemiluminescence. Fireflies glow by bioluminescence.

1.6 Electroluminescence is luminescence caused by electric current [4].

The photophysical process of the molecule is explained in the Jablonsky diagram (Fig. 2)

3

Fig. 2 Jablonski diagram

1.7 Fluorescence is the luminescence phenomena that occurred by supplying the energy in

the form electromagnetic radiation, usually ultraviolet light. The energy source excites an

electron of an atom from a lower energy level to an "excited" higher energy level and the

same falls back to a lower energy level by emitting photon (i.e) what is known as

fluorescence (s1 to s0) and it is allowed transition. The lifetime of an excited singlet state is

approximately 10-9 to 10-6 sec. Examples: fluorescent lights, the red glow of rubies in sunlight

[5].

1.7.1 Internal conversion is defined as radiationless processes where molecules in an excited

singlet state return to the ground state without the emission of a photon, converting all the

excitation energy into heat. The process called internal conversion. The life time of internal

conversion is 10-14 to 10-10. An example of this process is the quinine sulfate fluorescence, it

quenched by the use of various halide salts. In this case the excited molecule can de-excite by

increasing the thermal energy of the surrounding solvated ions.

1.7.2 Intersystem crossing is an isoenergetic radiationless transition between two electronic

states having a different multiplicity that is singlet (S) to triplet (T). It can occur within the

lifetime of an excited singlet state (10-10 to10-8 sec). It is facilitated by heavy metal ion (Ln

metal ion).

4

1.8 Phosphorescence is defined as when a molecule is placed in a rigid medium where

collisional processes are minimized, a radiative transition between the lowest triplet state and

the ground state is observed. This emission is called phosphorescence (T1 to S0). The decay

time of phosphorescence approximately equal to the lifetime of the triplet state (10-4 to 10

sec) as it originates from the lowest triplet state [6].

2. Lanthanides: In the recent years development of lanthanide based luminescent materials are playing an

important role due to f-f transitions. The excited states cannot be directly populated

efficiently because of their forbidden nature transition. To improve their emission intensity

requires a sensitizer that can populate the excited state manifold of the lanthanides by energy

transfer (ET). Efficient intersystem crossing is required (heavy metal ion effect or spin orbit

coupling). Mostly organic sensitizers have been used (due to their efficient absorption in the

UV region). Energy matching of the sensitizer states to those of lanthanides are of exited

states most importance [7] and the same in the pictorial view as shown in figure 3.

Fig. 3 Simplified mechanism for emission process

Lanthanides know as first inner transition series or third transition and come after lanthanum.

Lanthanides are classified as f block elements. Generally these are called as rare earths. These

are characterized by the filling up of the 4f energy levels which are not usually involved in

bonding. These highly electropositive elements have a common oxidation state of +3 and

generally resemble each other in their chemical and physical properties. They have a generic

symbol “Ln”. It contains 15 elements from lanthanum (La57) to lutetium (Lu71) [8]. In the

periodic table, covalent and ionic radii generally increase on descending a group due to the

presence of extra filled shells of electron. When we go from left to right across a period, the

covalent and ionic radii decrease. This is due to the extra orbital electrons incompletely shield

5

the extra nuclear charge. Thus the entire electrons are pulled in closer. The shielding effect of

electron decreases in the order s > p > d > f. the contraction in size from one element to

another is fairly small [9].

The photoluminescence properties of rare-earth (lanthanide) compounds have been attractive

for researchers from decades. Line-like emission of lanthanide is an attractive feature of

luminescent, which results in a high color purity of the emitted light. The emission color

depends on the lanthanide ion and it is also depend on layers (HT/ET material) of the device

which prefer to construct. Studies on these compounds have been limited to either inorganic

compounds (lanthanide phosphors) or molecular lanthanide compounds (for instance, the β-

diketonate complexes). The study of luminescent lanthanide compounds are used for different

a high potential applications (optical amplifiers, optical waveguides, OLEDs, etc.) [10].

Mostly the lanthanide materials are utilising for organic light emitting diodes (OLEDs) to

produce visible range light emission.

2.1 Classic DiekeDiagram for Lanthanide ions

The classic Dieke diagram of lanthanide ions is shown in Fig. 4.

6

Fig. 4 Classic Dieke diagram

3. Organic light-emitting diode (OLED):

Organic light-emitting diode is a display device that sandwiches carbon-based films between

two charged electrodes; those are cathode and anode respectively. The organic films consist

of a hole-injection layer, a hole-transport layer, an emissive layer and an electron-transport

layer. When the device is forward biased, electrons and holes moves from respective

electrodes, cathode and anode (ITO). The injected charges are recombined at emissive layer

to give emission in the form of light (EL). According to spin statistics the probability of

forming singlet states is 25% and the triplet states is 75%. The maximum fluorescent QE is

limited to 25% for the small organic molecule based OLEDs. To overcome the same

Baldoet.al., introduced phosphorescent materials (expected to harvest the triplet energy to the

ground state by light emission by spin orbit coupling, IQE can reach up to 100%) in the

OLEDs [11]. In the absence of Ln (III) ion complexes, only singlet excitons are proficient to

7

give light emission but not the triplet excitons. Ln based organic metallic complexes

incorporated in the emitting layer, both singlet and triplet excitons are utilized and which

leads to increase in the device efficiency. The heavy metal ion effect facilitates the energy

transfer from the singlet to triplet through ISC process and subsequently the emission arises

from the f level [12].

3.1 History of OLEDs:

In 1907, Captain Henry Joseph Round was demonstrated inorganic luminescence on a crystal

of carborandam [13]. Light emission from β-diketonates with lanthanide materials was first

reported by Weissmanin 1942 [14]. The EL from organic material such as acridine orange

has been observed first time by A Bernanose in 1955 [15]. In 1963 Pope reported single layer

organic EL device with anthracene crystals [16] after that the Helfrich and Schneider also

introduced single layer device [17]. In 1987, Tang and Vanshyke introduced high

performance two layer OLED by vacuum deposition of organic layers have low bias voltage

performance [18]. The dynamic work moved on OLEDs ofter this research work. In 1990,

Burrougheset al., observed electroluminescence from organic polymer [19].In organometallic

complex, ligand excitation energy is transferred to central metal ion through its triplet states

and produce emission. In general blue, green and red colors are essential for full colour

displays. Mixing of these colors produce the white color emission and it depends on host, HT,

ET materials along with their appropriate voltages [20].

3.2 There are mainly two types of OLEDS are available. Those are

(1) Passive OLEDs (2) Active OLEDs

Table 2. Types of OLEDs

Passive OLEDs Active OLEDs

Ø The organic layer is between strips of

cathode and anode that run perpendicular

Ø The intersections form the pixels

Ø Easy to make

Ø Use more power

Ø Best for small screens

Ø Full layers of cathode and anode

Ø Anode over lays a thin film transistor

(TFT)

Ø Requires less power

Ø Higher refresh rates

Ø Suitable for large screens

8

3.3 Architecture of OLEDs:

Fig. 5 OLED device structure

Substrate: clear plastic, glass, foil used as substrate in OLED.

Anode is source of holes. When a current flows through the device the holes will move from

anode.

Organic emissive layer is made of organic material which is using in middle of the device.

Cathode is source for electrons. When a current flows through the device the electrons will

move from cathode [21].

3.4 Advantages and Applications of OLEDs:

OLEDs are gained much importance due to their advantages such as longer life time, faster

switching on smaller size, environment friendly, low cost, low drive voltages, colour purity

and flexibility nature. Recently attractive results are reported on phosphorescent based

Organic light emitting diodes (OLED) due to their internal quantum efficiency (up to 100%).

The Ln based organometallic complexes are used in different applications such as cathode

ray tubes, Computer Screens, Keyboards, Digital Camera, air craft and space shuttles,

television screens, fluoro immune assay, biomedicine and related technology, biophysical

applications like receptors and sensing reagents of chiral biological substrates and photonic

crystals, full colour flat panel displays [22-23].

Usually Eu(III) complexes exhibit red emission in the region around 614nm due to 5D0-7F2

electronic transition (hyper sensitive). In order to obtain efficient emission, suitable designed

molecules (multifunctional ligand) have to be chosen and the same have to be incorporated in

suitable devices. In addition, the appropriate host materials have to be choosen and doping

concentration need to be optimized. In the case of phosphorescent based OLEDs one can

expect that the internal quantum efficiency (IQE) reach up to 100% (according to spin

statistics). However, the external quantum efficiency (EQE) is not that satisfactory, efforts

have been made to improve the EQE, and the different device structures have been

9

introduced. Charge carrier transportation and efficient recombination of the charge are more

important for the device efficiency (EQE). Drift mobilities of charges (holes and electrons) in

the device are strongly electric field and temperature dependent [24]. Lanthanide metal ions

almost exhibit sharp-emission bands because of the 4f shell shielded by their outer orbitals.

The Eu+3 metal ion shows 580, 592, 612, 652 and 703 nm emission lines corresponding f-f

transitions of 5D0-7F0, 5D0-7F1, 5D0-7F2, 5D0-7F3 and 5D0-7F4 (Fig. 6) [25].

Fig. 6 Energy level diagram of Eu(III) ion

4. Bipolar ligands:

The ligand which is having both donor and accepter capacity is known as bipolar ligand.

N

O

NN

Na

N-phenyl-N-(4-(5-(pyridin-4-yl)-1,3,4-

oxadiazol-2-yl)phenyl)benzenamine

N

N

N N

N

b

N-(4-(1-ethyl-1H-imidazo[4,5-

f][1,10]phenanthrolin-2-yl)phenyl)-N-

phenylbenzenamine

Fig. 7 Bipolar ligands a and b

10

The tittle compound, C25H18N4O (a), is a non-planar bipolar ligand containing triphenylamine

and 1,3,4-oxadiazole units. In the molecule, the benzene ring, the 1,3,4-oxadiazole ring, and

the pyridine ring are twisted slightly with respect to each other. It is well known that OLED

produces light via recombination of electrons and holes, which are injected from electrodes

on opposite sides of the device. Furthermore, the balance between the injection and

transportation of electron and hole carriers leads to a high luminescence efficiency. Because

triphenylamine and the 1,3,4-oxadiazol group possess good properties of hole transportation

and electron deficiency, respectively, the compound containing these two groups should be of

an increased electron affinity and transporting properties, resulting in a more balanced charge

recombination in the emissive layer [26]. Tris(dibenzoylmethanato)(2-4’-

triphenylamino)imidazo[4,5-f]1,10 phenanthroline) is the light-emitting center, hole-

transporting triphenylamine and electron-transporting phenanthroline fragments are

integrated into one molecule [27].

Based on the extensive literature study, in the present investigation a bipolar ligand has been

designed [multi functional ligand which is consist of phenanthroline, fluorene moiety and

triphenylamine-diphenylamine] and the same is utilized as a bipolar ligand for the Eu

molecular complex. The same is synthesized by the condensation of 1,10-phenanthroline-

5,6-dione, 4-(bis(4-(diphenylamino)phenyl)amino)benzaldehyde (TPA-DPA) and 9,9-

diethyl-9H-fluoren-2-amine.

5. Objectives of the work:

Although up to a great progress has been achieved in the development of green-emitters, full-

color-displays also require red and blue-emitters. In accordance with the energy-gap law, the

design and synthesis of efficient red emitters is intrinsically more difficult. Efforts have been

made to design and synthesis europium based molecular complexes as a red emitting

phosphor for OLEDs. From the literature survey we found these below tasks

(a) Design and synthesis of Eu based Lanthanide-luminophores (bright- monochromatic)

(b) Link the multifunctional ligands (Phen, Fl, TPA-DPA)

(c) Incorporate light-emitting luminophore (fluorene/β-diketone) in the antenna

(d) Fabricate Lanthanide-phosphors based OLEDs

(e) Improve the External Quantum efficiency (Above 5%)

11

6. Experimental Section:

6.1 General Information for synthesis:

All reactions were performed under inert (nitrogen) atmosphere. Solvents were carefully

dried and distilled from appropriate drying agents prior to use. Commercially (sigma Aldrich)

available reagents are used without further purification unless otherwise stated. All the

reactions was monitored by thin-layer chromatography (TLC) with silicagel 60 F254

Aluminium plates (Merk). Column chromatography was carried out using silica gel from

Aldrich (70 – 230 mesh, 60 Å).

6.2 Measurements:

1H-NMR and 13C-NMR spectra were recorded using a AV 400 Avance-III 400MHz FT-NMR

Spectrometer Bruker Biospin International, Switzerland, in deuterated chloroform and

deuterated dimethyl sulphoxide solution. Chemical shifts were quoted relative to

tetramethylsilane (TMS). Elemental analysis was measured by Elementar Analysen Systeme,

Germany/Vario EL. Mass spectra were recorded on an Perkin Elmer, USA/ Flexer SQ 300

M. The absorption spectrum was measured by using UV-visible spectrometer (Shimadzu

Corporation, Japan/UV-2450 Perkin Elmer, USA/Lamda 25). Thermo gravimetry analysis

were measured by DTA-Thermo Gravimetric Analyser (Shimadzu / DTG-60H).

6.3 Scheme of synthesis:

O2N

H2N

Br HNO3

1 1-1 1-2

1-3

NH2NH2.H2O

Pd/C, Ethanol, Reflux, 10h, 90%

KOH, KI, DMSO, OoC 12h, 71%

ACOOH, 70oC, 24h, 91%9H-fluorene 9,9-diethyl-9H

-fluorene9,9-diethyl-2-nitro

-9H-fluorene

9,9-diethyl-9H-fluoren-2-amine

12

N

CHO

N

CHO

II

N

CHO

NN

N DMF, POCl3 KI, KIO4

ACOOH

DPA

Dichloro benzene

4 4-1 4-24-3

TPA-DPA

N N

O O

H2N NH4OAc

Glacial AcOH, Reflux

N N

NNN

CHO

NNN

NN

Phen-Fl-TPA-DPA

2-1 1-3

4-3

TPA-DPA

O

OEu

Cl

6H2O

Cl

Cl

3

NaOH, Ethanol

H2O,RT, 60oC O

O

Eu

OH2

OH2

Eu (TTA) 3 .2H2OTris (thenoyltrifluoroacetone) Europium (III) hydrate

TTA

Phen-Fl-TPA-DPA

THFNN

N N

N

3O O

Eu

F

F

N N

FF

S

S

S

FF

F

FF

Thenoyltrifluoroacetone

Europium chloride hexahydrate

Eu(TTA)3 Phen-Fl-TPA-DPA

Fig. 8 Scheme of synthesis for designed new efficient red emitter [28-30]

13

6.4 Experimental Procedure:

1) Synthesis of 9,9-diethyl-9H-fluorene (1-1):

The powdered potassium hydroxide (KOH) (1.4g, 25.30mmol, 4.2eq) was added to a solution

of Fluorene (1g, 6.024mmol, 1eq) in DMSO (25mL) and added 1-bromo ethane (0.97mL,

13.25mmol, 2.2eq) and KI (0.09g, 0.602mmol, 0.1eq) at OoC. The reaction mixture (RM)

was stirred for 12hrs at room temperature and the progress of the reaction was monitored by

TLC (1:9 EtoAc: Hexane, Rf is 0.75). RM was pour into ice-cold water then extracted with

chloroform (3×30mL). The combined organic layer was washed with brine and diluted

hydrochloric acid (HCL) solution followed by drying with sodium sulphate, solvent

evaporated to get 1.1g crude product with mixture of compounds. Purification carried out by

using silica gel (100-200 mesh, EtoAc: Hexane 2:98) to a yield 1-1 a whitish color solid with

950mg (71%).

1H-NMR Data (CdCl3, 400MHz): δ 7.75-7.73 (m, 2H), 7.42-7.37 (m, 2H), 7.37-7.34 (m, 2H),

7.38-7.27 (m, 2H), 2.05 (q, 4H) and 0.34 (t, 6H).

2) Synthesis of 9,9-diethyl-2-nitro-9H-fluorene (1-2):

Into a clean two neck round bottom flask pour 1-1(0.2g, 0.899mmol) and added acetic acid

(1.6mL) solution at RT. This mixture was heated to 50oC then added nitric acid (0.2g,

5.411mmol) drop wise. The resulting mixture was stirred for 24hrs at 70oC and the progress

of the reaction was monitored by TLC (1:9 EtoAc: Hexane, Rf is 0.5). RM was cool to RT

and poured into water then basified with diluted sodium hydroxide solution up to pH 6

(neutral), extracted with ethyl acetate combined organic layer was washed with brine

followed by dried with anhydrous sodium sulphate, solvent was evaporated to get crude

compound. This was washed with hexane and diethyl ether simultaneously to get 1-2

(220mg, 91%) with brick yellow color solid.

1H-NMR Data (CdCl3, 400MHz): δ8.29-8.15 (m, 3H), 7.81-7.74 (m, 2H), 7.47-7.35 (m, 2H),

2.10-2.06 (m, 4H) and 0.38-0.33 (m, 6H).

3) Synthesis of 9,9-diethyl-9H-fluoren-2-amine (1-3):

To a stirred solution of 1-2 (200mg, 0.749mmol) in ethanol (15 mL) added hydrazine

monohydrate (0.5 mL) at RT. Then palladium on carbon (Pd/C, 10% w/w) (0.05g) was added

under nitrogen atmosphere and resulting mixture was reflux (85oC) for 10hrs. The progress of

14

the reaction was monitored by TLC (EtOAc: Hexane 2:8Rf is 0.6, ninhydrin active) and RM

was filtered through celite bed followed by concentrated to get 190mg of 1-3 crude

compound. This was purified with column chromatography by using silica gel (100-200

mash). The compound eluted with 8% ethyl acetate in pet ether and solvent concentrated to

get 160mg (90%) 1-3 pure compound.

1H-NMR Data (CdCl3, 400MHz): δ 7.58-7.56 (m, 1H), 7.51-7.49 (m, 1H), 7.30-7.28 (m, 1H),

7.26-7.20 (m, 2H), 6.69-6.67 (m, 2H), 3.65 (bs, 2H), 2.03-1.91 (m, 4H) and 0.34 (t, 6H).

4) Synthesis of 4-(diphenylamino)benzaldehyde (4-1) :

Dimethylformamide (DMF) (1.71mL, 22.04mmol) was taken in a clean-dried two neck round

bottom flask and added drop wise phosphorous oxy chloride (2.05ml, 22.04mmol) at 5oC.

After 30min, triphenylamine (TPA) (2g, 8.163mmol) in DMF (15mL) was added drop wise

to reaction mixture at same temperature. The RM was appears in brick yellow color and the

progress of the reaction was monitored by TLC (EtOAc in Hexane 1:9, Rf-0.4). The resulting

mixture was stirred for overnight at RT, then poured into water and neutralized with diluted

sodium hydroxide solution (up to pH 6). Then extracted with chloroform and washed with

brine solution followed by dried with sodium sulphate and removal of solvent to get 2.2g of

crude (4-1). The crude product was washed with diethyl ether: hexane (3:7) mixture solvent

and recrystallization in ethanol to get 2g pure 4-(diphenylamino)benzaldehyde(4-1) (90%)

with pale yellow colored fine solid.

1H-NMR Data (CdCl3, 400MHz): δ 9.82 (s, 1H), 7.70 (d, 2H), 7.38-7.34 (m, 2H), 7.25-7.24

(m, 2H), 7.20-7.15 (m, 6H), 7.03 (d, 2H).

13C-NMR Data (CdCl3, 100MHz): δ 153.3, 146.1, 131.3, 129.7, 129.0, 126.3, 125.1, 119.3.

EI-mass: m/z 274 (M++1)

5) Synthesis of 4-(bis(4-iodophenyl)amino)benzaldehyde (4-2):

Under rapid stirring, 4 (2.73 g, 10 mmol) was dissolved in glacial acetic acid (10 mL) and KI

(3.32 g, 20 mmol) and KIO3 (6.42 g, 30 mmol) were added; the reaction mixture was stirred

for 3 h at 700 C. After cooling, the solid was filtered off and washed thoroughly with water

(50 mL) and dichloromethane (100 mL). The aqueous phase was extracted several times with

dichloromethane. The combined organic phases were washed with a diluted ammonia

solution (10%) until pH becomes nearly 8, with a saturated NaHCO3 solution, and with

15

saturated brine and dried over MgSO4. After removal of the solvents, the crude compound

was stirred for 15 min in boiling ethanol (50 mL); the solution was cooled, and the pure

product was isolated by filtration (4.2 g, 80%). Yellow solid,

1H-NMR Data (DMSO, 400MHz): δ 9.859 (s, 1H), 7.72 (d, 2 H), 7.64 (d, 4H), 7.07 (d, 2H),

6.91 (d, 4H).

6) Synthesis of 4-(bis(4-(diphenylamino)phenyl)amino)benzaldehyde (4-3) (TPA-DPA):

In a 250mL round bottom flask, 4-[N,N-di(4-iodophenyl)amino]- benzaldehyde (1g,

1.9mmol), diphenylamine (0.98g, 5.7mmol), potassium carbonate (2.09g, 15.2 mmol) copper

iodide (0.28g, 1.52mmol) and 18 – crown – 6 (0.01g, 0.38mmol) were reflexed in 1,2 –

dichlorobenzene (15mL) for 48 hrs, under nitrogen atmosphere. The inorganic components

are filtered while hot and then the product was precipitated in methanol. The crude product

was purified by column chromatography on silica (petroleum ether: dichloromethane = 1:1,

v/v) to afford the product as yellow powder (yield: 59 %).

1H-NMR Data (DMSO, 400MHz): δ 9.815 (s, 1H), 7.22 (t, 9H), 7.05 (d, 9H), 6.96 (d, 3H),

6.81 (t, 4H).

13C NMR data (100MHz, DMSO-d6): δ 190.97, 141.45, 140.82, 140.56, 140.15, 132.10,

130.02, 129.80, 127.91, 125.16, 125.11, 123.75, 115.40.

FT-IR Data (KBr): γC-C = 1501(aromatic), γC-N = 1308 (aromatic), γC-H (S) = 695

7) Synthesis of N1-(4-(diphenylamino)phenyl)-N1-(4-(1-(9,9-diethyl-9H-fluoren-2-yl)-

1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl)-N4,N4-diphenylbenzene-1,4-

diamine (Phen-Fl-TPA-DPA):

1-3 (0.75g, 3.171mmol) was added to a stirred solution of 4-3 (1.75g, 2.883mmol) in glacial

acetic acid (30mL) at room temperature. To this reaction mixture subsequently ammonium

acetate (2.2g, 28.83mmol) and 2-1 (0.60g, 2.883mmol) was added. Then resulting mixture

was stirred for 12hrs at 110oC. The progress of the reaction was monitored by TLC (MeOH

in Chloroform 1:9, Rf-0.2). The RM was pour into minimum amount of water and then

ammonium hydroxide solution was added. Then the formed solid was filtered and dissolved

in dichloromethane, followed by dried with anhydrous sodium sulphate and the solvent was

evaporated to get 3g crude compound. The resultant compound was purified with column

16

chromatography by using silica gel (100-200 mesh), eluent with 5% methanol in chloroform

and the solvent was evaporated and dissolved in minimum amount of THF solution added

excess of hexane solvent, the pale yellow color solid was formed. After settled of solid,

decant and repeated this process three more times and get compound- Phen-Fl-TPA-DPA, 1g

solid.

1H-NMR Data (CdCl3, 400MHz): δ 9.21-9.16 (m, 2H), 9.03 (d, 1H), 7.91 (d, 1H), 7.87-7.76

(m, 3H), 7.62-7.45 (m, 8H), 7.25-7.16 (m, 9H), 7.14-7.06 (m, 11H), 7.01-6.96 (m, 11H) 2.05

(q, 4H), 0.42 (t, 3H), 0.24 (t, 2H).

EI-mass: m/z 1019.24 (M++1)

FT-IR Data (KBr): γN-H = 3426, γC-H = 3032 (aromatic), γC-C =1490 (aromatic), γC-N = 1310

(aromatic), γC-H (S) = 695

8) Synthesis of Eu (TTA)3.2H2O:

Taken a 100 mL of two neck round bottom flask with balloon contained adaptor and poured

TTA (Thenoyltrifluoroacetone) (1g, 4.504 mmol, 3eq) dissolved in absolute ethanol (20 mL)

and then sodium hydroxide (0.186g, 4.650 mmol, 3.1eq) solution is added. Then the reaction

mixture was stirred for 30min and Europium chloride hexahydrate (EuCl3.6H2O) (0.549g, 1.5

mmol, 1eq) solution added and after some time 50 mL of deionised water is added. The

reaction mixture was stirred for overnight at 60oC.

The yellowish white precipitate was observed and the precipitate was filtered, dried in

vaccum. The obtained powder was dissolved in minimum amount of THF and then filtered

through cotton filled pipette. Pentane layer is made in the clear THF solution and kept in the

freezer for crystallisation. The purified compound is dried to get 0.95 g (74.8%)oftris

(thenoyltrifluoroacetone) Europium (III) hydrateand used for further analysis.

1H-NMR Data (CdCl3, 400MHz): δ7.45 (s, 3H), 6.37 (d, 6H), 3.59 (s, 3H).

CHNS Analysis: Anal. Calc. for C24H16EuF9O8S3: C, 33.85; H, 1.89; S, 11.30. Found: C,

33.60; H, 1.37; S, 10.89%.

FT-IR Data (KBr): γC-O = 1617 (aromatic), γC=C =1539 (aromatic), γC-N = 1305 (aromatic).

17

9) Synthesis of Eu(TTA)3 Phen-Fl-TPA-DPA:

Taken a 50mL two neck round bottom flask with nitrogen containing balloon contained

adaptor and poured Eu (TTA)3.2H2O (83g, 0.098mmol, 1eq) dissolved in dry tetrahydrofuron

(THF) (10mL). The compound- Phen-Fl-TPA-DPA (100g, 0.098 mmol, 1eq) dissolved in

THF (10mL) and added to stirred solution of reaction mixture (RM) then stirred for 12hrs at

room temperature. The resulting mixture was concentrated and dissolved in minimum amount

of THF and added excess of hexane to get solid product. After settled of solid, decant and

repeated it another two times and dried to get pale yellow color solid with mg 150mg (84%).

The obtained solid was dissolved in minimum amount of THF and then filtered through

cotton filled pipette. Pentane layer is made in the clear THF solution and kept in the freezer

for crystallisation.

EI-mass: m/z 1834.9 (M++1)

CHNS Analysis: Anal. Calc. for: C96H67EuF9N7O6S3; C, 62.88; H, 3.68; Eu, 8.29; F, 9.32; N,

5.35; O, 5.23; S, 5.25%. , Found: C, 61.81; H, 3.08; Eu, 7.80; F, 9.85; N, 5.25; O, 5.01; S,

5.45.

FT-IR Data (KBr): γN-H = 3436, γC-O = 1600 (aromatic), γC-C =1501 (aromatic), γC-N = 1305

(aromatic), γC-H (S) = 695

7. Results and Discussion:

The designed Eu-complex (Eu(TTA)3 Phen-Fl-TPA-DPA) is successfully synthesised and

characterised. The photophysical properties were measured with UV-Visible and

spectrofluorimetry analysis. The thermogravimetric analysis (TGA) shows that the compound

is thermally stable (278oC (10%)) and it is good enough to fabricate the OLED device using

the synthesised Eu(III)-complex.

The digital photographs was taken under long UV lamp (365 nm) for the corresponding Eu-

complex and Eu (TTA)3 and the same has been shown in Fig. 9.

18

Fig. 9 Europium complex and Eu(TTA)3 under normal light and UV-light (365nm)

Fig 10. The UV-visible absorption spectra of Europium complex and Eu(TTA)3 in

chloroform solution (concentration 10-5M).

19

The UV-visible absorption spectra of Ligand (L = Phen-Fl-TPA-DPA), Europium complex,

and Eu(TTA)3 in Dichloromethane solution (concentration is 10-5M) is shown in Fig. 10. The

absorption spectrum of Ligand shows absorption from 250 to 450 with λmax. 360 nm, 275 nm,

these bands were attributed to the π → π* transitions of the ligands. Similarly the Eu (TTA)3

Phen-Fl-TPA-DPA and Eu (TTA)3 shows the peak maxima at 341nm, 278 nm and 340nm

and 275nm, respectively. It indicating that the efficient energy transfer from the Ligand

molecule to central Eu(III) metal ion.

Fig. 11 The photoluminescence emission spectra of Eu(TTA)3.2H2O, Eu(TTA)3Phen-FL-

TPA-DPA and Phen-Fl-TPA-DPA

The photoluminescence emission spectra of Eu(TTA)3Phen-FL-TPA-DPA exhibits 5D0-7F2

(J=0-4) transitions of Eu(III) ion. The consist of 5D0-7Fo transition (580nm, single peak) in

the emission spectra indicates that the all Eu3+ ions occupy a site of the same symmetry and

experience the same crystal field perturbation [31]. The most intense induced electronic

dipole transition is 5D0-7F2 observed at 614 nm and this intensity is sensitive to the chemical

environment. The photoluminescence emission spectrum of ligand (Phen-FL-TPA-DPA)

exhibits a broad emission peak at 523 nm due to TPA-DPA.

20

Fig. 12 Thermogravimetric analysis (TGA) for Phen-Fl-TPA-DPA and Eu(TTA)3Phen-FL-

TPA-DPA

The thermogravimetric analysis were measured under nitrogen atmosphere with 10oC per

minute for Phen-Fl-TPA-DPA and Eu(TTA)3Phen-FL-TPA-DPA (fig. 12). The compound

Phen-Fl-TPA-DPA shown 20% thermal decomposition at 370oC and Eu(TTA)3Phen-FL-

21

TPA-DPA shown 10% decomposition at 278oC. These are indicating that synthesised Eu-

Complex have above 250oC decomposition. It is thermal stable enough to be fabricate device.

8. Summary and conclusions: Ø The expected efficient red emitting molecular material based on Eu-complexes with

charge-transporting antenna was successfully synthesized and characterized by NMR,

Mass and elemental analysis.

Ø Form the UV-visible and PL spectral analysis, we observed that the efficient energy

transfer from the Ligand molecule to central Eu(III) metal ion.

Ø TGA is shown thermal stable (278oC (10%)) enough to be fabricate device.

9. Scope for the future work: Ø The HOMO and LUMO levels of the ligand and the complexes will be determined by

using cyclic voltammetry.

Ø Glass transition temperature will be determined by using DSC analysis.

Ø From the synthesised Eu-complex, it is expected that the TPA can transport the hole

(HT) and phenanthroline can transport the electron (ET) in the OLED device

Ø The synthesised Eu(III)-complex will be incorporated with suitable OLED device

structure.

Ø The electroluminescence properties of the proposed device will be measured.

22

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